1. Field of the Invention
The present invention relates to a sheet processing apparatus capable of moving a sheet to a processing position and processing the sheet at the processing position, and to an image forming apparatus having the sheet processing apparatus.
2. Description of the Related Art
Some conventional image forming apparatuses which form an image on a sheet have a sheet processing apparatus which bundles sheets on which images are formed in an apparatus body, binds and folds the same into a booklet form. As such a sheet processing apparatus, an invention of US2007/0060459 is disclosed. According to the sheet processing apparatus described in US2007/0060459, sheets are sequentially received by a tray, the sheets are bound into a bundle and aligned, central portions of the sheets are bound, the central portions are pricked with an thrusting member and pushed into a nip of a pair of folding rollers, and the pair of folding rollers fold the sheet bundle while conveying the bundle.
The operation of the conventional sheet processing apparatus will be described using FIGS. 17 to 19. As illustrated in FIG. 17, the sheet processing apparatus first aligns a plurality of sheets by a collecting portion (accommodating guide) 803 as the tray and then, the sheet processing apparatus binds the central portions of the sheets in the conveying direction with a staple. Next, the central portion of the sheet bundle is pricked with a folding plate (thrusting) member 830 as the thrusting member, and the central portion is pushed into a nip between a pair of first folding rollers 810a and 810b. The sheet bundle is fold by the pair of folding rollers 810a and 810b, then the sheet bundle is conveyed a pair of first folded sheet conveying rollers 811a and 811b, and a pair of second folded sheet conveying rollers 812a and 812b, and the sheet bundle is stopped.
The folded portion is nipped by the pair of first folded sheet conveying rollers 811a and 811b, and the pair of second folded sheet conveying rollers 812a and 812b, a press rollers are moved along the crease of the sheets (in a direction orthogonal to the conveying direction), thereby reinforcing the folded portion. With this, the sheet bundle is folded from center, and a center-folded sheet bundle (simply referred to as a “folded sheet bundle”, hereinafter) is completed. Then, the sheet bundle is conveyed and discharged into a folded bundle discharge tray 840.
In recent years, sheets are diversified, and image quality level of the image forming apparatus is enhanced. For example, it is possible to print on a paper sheet such as a special sheet whose surface is processed such as a coated paper, or a paper sheet having a wide range of grammage to which the sheet is adapted (thin weak paper or thick firm paper).
However, as illustrated in FIG. 18, when weak sheets are stacked on an inclined tray or when the stacked sheets are moved, the following problems may occur. When a sheet bundle is moved to a binding position (processing position) of a stapler 820 located above the stacking position, if the sheet bundle is lifted only by a sheet receiving member 805, the weight of the sheet bundle may not be supported and the sheet bundle is buckled. As a result, the binding position of a staple is deviated by the buckled amount as illustrated in FIG. 19.
Especially in an upright path aligning structure which aligns sheets at a substantially vertical sheet stacking portion, the above circumstance is significant. As a solution, the sheet stacking portion may be disposed substantially horizontally so that the sheets are not affected by the own weight, but this causes the apparatus to be increased in size in the lateral direction and as a result, the installation area of the apparatus is increased.